1. Field of the Invention
The present invention relates to a plunger switch used as a brake lamp switch of an automobile and so on, and more particularly, to a plunger switch having a self-adjusting mechanism capable of automatically adjusting an operating position of a plunger after being mounted in a predetermined mount position.
2. Description of the Related Art
In a plunger switch used as a brake lamp switch of an automobile, a plunger which partly projects from a housing of a switch body is urged by a brake pedal as an outer actuator and a compression spring in the housing, thereby bringing and separating a movable contact, which reciprocates while following the plunger, in contact with and from a fixed contact in the housing to light and put out a brake lamp through a terminal led out from the fixed contact. In other words, since the brake pedal held in a release position by a strong spring force presses the plunger in and separates the movable contact in the housing from the fixed contact, the brake lamp is held in a light-out state at this time. However, when a driver presses on the brake pedal, since the brake pedal is moved in the projecting direction of the plunger, the press-in force is removed. Accordingly, the plunger is pushed back by the compression spring in the housing, the movable contact is brought into contact with the fixed contact, and the brake lamp is lighted.
Even if such plunger switch for a brake lamp is mounted in a predetermined position of a mount panel (bracket), since a non-negligible error is liable to occur in the relative position to the brake pedal, an adjusting mechanism capable of setting the plunger in a proper initial position relative to the brake pedal on and after mounting the plunger switch to the mount panel is needed to operatively connect the plunger switch to the brake pedal with certainty. Various kinds of plunger switches each having such adjusting mechanism have been suggested heretofore, and a plunger switch disclosed in U.S. Pat. No. 4,316,065 is given as an example of conventional art which is provided with a self-adjusting mechanism capable of automatically adjusting an operating position of a plunger after being mounted, has a simple structure and can hold down costs.
In other words, since a movable device for holding a movable contact is connected to a plunger in a housing in this conventional art, the movable contact can be brought into contact with and separated from a fixed contact by reciprocating the movable device through the plunger in the housing. Furthermore, since coupling portions of the plunger and the movable device are formed by a ratchet and a wire spring or the like disengageable from the ratchet, when an overload is applied to the plunger owing to an error in the relative position between the plunger and the brake pedal after the housing is mounted to a mount panel, the plunger is pressed in even after the position of the movable device is regulated, the coupling portions of the plunger and the movable device are displaced from each other, and the plunger is set in the proper initial position for eliminating the error in the relative position to the brake pedal. In short, the operating position of the plunger is automatically adjusted (self-adjust) within the range of the ratchet.
However, since the plunger and the movable device are coupled to each other in the housing of the above-mentioned conventional plunger switch, when the self-adjusting operation is performed and the wire spring or the like is engaged with and disengaged from the ratchet, there is a fear that reliability of the product will be lowered by, for example, faulty conduction caused by the adhesion of shavings of the ratchet to the movable contact and the fixed contact in the housing.